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J Appl Physiol 104: 521-533, 2008. First published September 13, 2007; doi:10.1152/japplphysiol.00729.2007
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End-expiratory and tidal volumes measured in conscious mice using single projection x-ray images

Stephen J. Lai-Fook,1 Pamela K. Houtz,1 and Yih-Loong Lai2

1Center for Biomedical Engineering, University of Kentucky, Lexington, KY and 2Department of Physiology, National Taiwan University College of Medicine, Taipei, Taiwan

Submitted 6 July 2007 ; accepted in final form 12 September 2007

The evaluation of airway resistance (Raw) in conscious mice requires both end-expiratory (Ve) and tidal volumes (Vt) (Lai-Fook SJ and Lai YL. J Appl Physiol 98: 2204–2218, 2005). In anesthetized BALB/c mice we measured lung area (AL) from ventral-to-dorsal x-ray images taken at FRC (Ve) and after air inflation with 0.25 and 0.50 ml ({Delta}VL). Total lung volume (VL) described by equation: VL = {Delta}VL + VFRC = KAL1.5 assumed uniform (isotropic) inflation. Total VFRC averaged 0.55 ml, consisting of 0.10 ml tissue, 0.21 ml blood and 0.24 ml air. K averaged 1.84. In conscious mice in a sealed box, we measured the peak-to-peak box pressure excursions ({Delta}Pb) and x-rays during several cycles. K was used to convert measured AL1.5 to VL values. We calculated Ve and Vt from the plot of VL vs. cos({alpha} – {phi}). Phase angle {alpha} was the minimum point of the Pb cycle to the x-ray exposure. Phase difference between the Pb and VL cycles ({phi}) was measured from {Delta}Pb values using both room- and body-temperature humidified box air. A similar analysis was used after aerosol exposures to bronchoconstrictor methacholine (Mch), except that {phi} depended also on increased Raw. In conscious mice, Ve (0.24 ml) doubled after Mch (50–125 mg/ml) aerosol exposure with constant Vt, frequency (f), {Delta}Pb, and Raw. In anesthetized mice, in addition to an increased Ve, repeated 100 mg/ml Mch exposures increased both {Delta}Pb and Raw and decreased f to apnea in 10 min. Thus conscious mice adapted to Mch by limiting Raw, while anesthesia resulted in airway closure followed by diaphragm fatigue and failure.

bronchoconstrictor; methacholine aerosol; body plethysmography


Address for reprint requests and other correspondence: S. J. Lai-Fook, Center for Biomedical Engineering, Wenner-Gren Research Laboratory, Univ. of Kentucky, Lexington, KY 40506-0070 (e-mail: laifook{at}email.uky.edu)




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